1. Field of the Invention
The present invention relates to a composition suitable for preparing a reactive hot melt composition, and the reactive hot melt composition made therefrom. Advantageously, the reactive hot melt composition can be used as a hot melt adhesive, in particular, a film-form adhesive having a determined thickness. The hot melt adhesive is useful for adhering electronic parts such as integrated circuit (IC) chips to a substrate as well as for producing multilayer electronic interconnect circuits. Suitable substrates include ceramics, metals, plastics, and the like, and the reactive hot melt compositions of the present invention have good adhesion to these surfaces.
2. Description of the Related Art
A hot melt adhesive gives high speed adhesion because adhesion is obtained through a physical change in the adhesive. A thermoplastic resin composition that is solid at room temperature is melted, applied to an adherend, and then cooled until it solidifies. By utilizing this property, manufacturing productivity can be increased. Hot melt adhesives have been mainly used in packaging and woodworking applications, with wide use in the electric and electronic fields more recently.
However, conventional hot melt adhesives have poor adhesion at temperatures above their melting points and low heat resistance, which limits the use of the hot melt adhesives in the electric and electronic applications. For example, adhesives used for fixing a lead pin to a lead frame of an IC chip are heat laminated and then placed in a high temperature environment of 230 to 260.degree. C., which is higher than the temperature for soldering. Since conventional hot melt adhesives cannot maintain sufficient adhesion at these temperatures, they cannot be used in these applications.
Reactive hot melt adhesives, which crosslink after bonding, are known for having improved heat resistance. Examples of known reactive hot melt adhesives include the following:
(1) A moisture-curing hot melt adhesive comprising a polymer which has an isocyanate group (see U.S. Pat. No. 5,418,288 corresponding to JP-A-6-158017, etc.); PA1 (2) A silanol condensation type hot melt adhesive comprising a polymer which has a silyl group (see JP-A-5-320608, etc.); PA1 (3) A radical polymerization type hot melt adhesive comprising a polymer which has an acryloyl group (see JP-A-63230781, etc.); PA1 (4) A thermosetting hot melt adhesive comprising a polymer which has a glycidyl group, and a phenol resin (see JP-A-6172731, etc.); and PA1 (5) A method for crosslinking a hot melt adhesive by irradiation after application of the adhesive (see JP-A-6-306346, etc.). PA1 (i) In general, the crosslinking reaction is slow, and a lengthy post curing is necessary (for example, in the case of (1) and (2) above); PA1 (ii) Some of the adhesives require moisture (usually obtained from the air) for the crosslinking reaction, and are not suitable for use in environments where the adhesive has limited exposure to air during curing (for example, in the case of (1) above); PA1 (iii) Some of the adhesives generate water as a by-product, which may have adverse effects, such as the deterioration of adhesion with time, particularly for bonding electronic parts. (for example, in the case of (2) above); PA1 (iv) Some of the adhesives require a solvent for forming a film adhesive, and the residual solvent may have adverse effects (for example, in the case of (1) to (4) above); PA1 (v) In general, the crosslinking reaction proceeds gradually even when the adhesives are stored at room temperature (about 25.degree. C.), and the adhesives have poor shelf stability (for example, in the case of (1), (2) and (3) above); and PA1 (vi) A radiation crosslinking adhesive is not suitable for use with adherends that do not readily permit or tolerate radiation exposure (in the case of (5) above).
However, the reactive hot melt adhesives disclosed in these references still have the following drawbacks:
It would be desirable to have a composition that can yield a reactive hot melt adhesive that does not suffer from these drawbacks, as well as the resulting reactive hot melt composition, especially if it can be provided in film form.